System for controlling a compressor of an air conditioner for motor vehicles

Abstract

A vehicle speed detector is provided for producing a vehicle speed signal and a load detector detects load on an engine to produce a load signal. A map storing a plurality of reference load values dependent on vehicle speeds is provided, and a reference load value is derived from the map in accordance with the vehicle speed signal. The load signal is compared with a derived reference load value. When the load is larger than the derived reference load value, a clutch for a compressor is disengaged to stop operation of the compressor.

What is claimed is: 
     
       1. In a system for controlling a compressor of an air conditioner for a vehicle powered by an engine, the system having an electromagnetic clutch for coupling the engine with the compressor, an electrically operated switch provided in a circuit for engaging the clutch, vehicle speed detecting means for detecting vehicle speed and for producing a vehicle speed signal corresponding to the vehicle speed, and engine load detecting means for detecting pressure in an intake manifold of the engine and for producing an actual pressure signal corresponding to the actual pressure in the intake manifold, the improvement comprising: reference load characteristic memorizing means memorizing a characteristic comprising a desired pressure signal representing a continuously decreasing function of decreasing of the vehicle speed signal,   decision means for reading out a value of the desired pressure signal from the reference load characteristic memorizing means corresponding to and in response to the vehicle speed signal,   comparator means for comparing the actual pressure signal with the read out value and for producing a clutch disengagement signal when the actual pressure signal is larger than the read out value; and   control means responsive to the clutch disengagement signal for opening the electrically operated switch to stop operation of the compressor so as to reduce the load on the engine to increase the power for driving the vehicle.   
     
     
       2. The system according to claim 1, wherein said memorizing means sets said desired pressure signal, when the compressor is stopped, corresponding to an off-reference pressure of a higher load value than an on-reference pressure at the same vehicle speed when the compressor is on, so as to provide a hysteresis between on and off conditions of the compressor.